Research shared by a midwifery student

Postdates Pregnancy: What Are We Waiting For?

The following is written to outline some points of consideration regarding pregnancies progressing beyond 42 weeks in length.

Postdates pregnancies are often treated as conditions of absolute risk and result in much intervention. While interventions may be required in specific cases, induction of labor is commonly justified by referring to unreliable means of assessing gestational length. After this classification, labor is often induced with aggressive methods which cause undue stress on the unborn, while little consideration is given to equally-effective and minimally invasive natural methods.

It has been discovered that as many as half of “postdates” women are really at term. [1]

Our dating methods and definition of the average length of pregnancycould stand to be reconsidered. It has been discovered that the average gestational length exceeds 280 days. [2] Also, “ultrasound dating has a margin of error greater than dating by LMP.” (p. 186) [2] If both the methods for determining age and the commonly-accepted “average” are both highly innaccurate, we are subjecting women to unnecessary stress by implying that they are outside the realm of normal when, in fact, they are experiencing a very normal pregnancy.

While ultrasound dating may be more accurate when performed between 6 and 12 weeks menstrual age, [2] many obstetricians are not “trained to do or interpret sonograms and over 70% were performed by their assistants”. [1] This is a possible correction within the system which has not been taken into practice. Thus, “components of the biophysical profile will continue to be measured against equally poorly validated fetal surveillance tests.” [1]

Even in cases of postmaturity, induction may pose a greater risk than any concerns related to the fetus’ gestational age.

“…There is absolutely no study, no evidence whatsoever, that routine induction at any gestational age improves perinatal outcome.” [2] It has been proven that induction and augmentation may increase chance of infection, fetal stress, etc., [4, 11] and the findings of a study comparing early versus late induction were: “Paradoxically, induction succeeds best in women with ripe cervixes, but these are the women most likely to begin labor shortly. If the goal is preventing postmaturity syndrome, these women may not need induction. ‘[W]e now postpone the induction of labor in post-term cases, as the risk in monitoring the natural course, certainly up to day 308, seems minimal.’” [11]

This tells us something very important. When inductions “fail” or do not succeed to induce labor within OUR time frame, it is safe to assume that the mother’s body is simply not responding because the time is not right. If one had never intervened, then, labor and birth would proceed at the rates which were intended in the first place.

Tests, such as the antepartum non-stress test (NST) are known to have a 40-80% false-positive rate. The conditions for which it screens are largely incurable, which gives one cause to wonder what the exact advantage is of a test with such a high false-positive rate which “can lead to undue psychological strain on the woman and her family, unnecessary intervention, and possible iatrogenic problems from the intervention.” [10]

The safest option is to wait, followed by the option of using more natural means of inducing labor.

Rather than contribute to anxiety, discontentment, and possibly danger to the mother and baby, care providers ought to watch and wait, knowing that indications for induction/augmentation will present themselves if they are truly necessary. Natural induction methods are to be considered first, although resulting stress on the fetus cannot be dismissed.

“In the absence of signs [of growth retardation] and in otherwise uncomplicated pregnancies, the safest management of prolonged pregnancy is to await the spontaneous onset of labor.” [3]

It has been proven that:

Nipple stimulation ripens the cervix and shortens pregnancy [8-9]

Membrane stripping does not affect the mode of delivery when used to shorten labor [5-7]

From these findings, we may conclude that many a healthy mother carrying a pregnancy lasting longer than 42 weeks may do so more safely under limited management without increased risk to her or her child. If it becomes necessary, intervention ought to begin in its most minimal form, progressing to more invasive means with the correct indications and with full disclosure of the risks to the parents.

CITATIONS:

Shearer MH and Estes M. A critical review of the recent literature on postterm pregnancy and a look at women’s experiences. Birth 1985;12(2):95-111.